Thin film room-temperature electron emitter

ABSTRACT

A vacuum enclosure containing an anode and a cathode, wherein a first embodiment of the cathode comprises a continuous thin film of semiconductive material deposited on an electrically insulating substrate and adapted to have a potential difference placed thereacross. A break in the film exists so as to produce a high impedance to the flow of current. A second embodiment of the cathode comprises a noncontiguous thin film of semiconductive and metallic material deposited at random in small droplets on a substrate and adapted to have a potential difference placed thereacross.

United States Patent [72] Inventor Sidney T. Smith Alexandria, Va. {21] Appl. No. 802,527 [22] Filed Feb. 26, 1969 [45] Patented Oct. 5, 1971 [73] Assignee The United States of America as represented by the Secretary of the Navy [54] THIN FILM ROOM-TEMPERATURE ELECTRON EMITTER 12 Claims, 5 Drawing Figs.

[52] U.S.Cl 315/94, 313/310, 313/31 1, 313/326, 313/346, 317/234 S [51] Int.Cl I-I0lj1/14, H01 j 19/06 [50] Field of Search 307/293, 308; 315/169, 94; 317/234 (8), 234 (8.1 313/311, 336, 346, 355, 235, 310, 326, 329, 341, 342

[56] References Cited UNITED STATES PATENTS 3,098,168 7/1963 Aigrain 313/346 3,277,313 10/1966 Unterkofler 313/346 X 3,359,448 12/1967 Bashara 313/326 FOREIGN PATENTS 782,063 4/1968 Canada 317/234 1,004,396 9/1965 Great Britain 317/234 Primary Examiner-Roy Lake Assistant Examiner-E. R. La Roche Attorneys-R. S. Sciascia and A. L. Branning ABSTRACT: A vacuum enclosure containing an anode and a cathode, wherein a first embodiment of the cathode comprises a continuous thin film of semiconductivc material deposited on an electrically insulating substrate and adapted to have a potential difference placed thereacross. A break in the film exists so as to produce a high impedance to the flow of current. A second embodiment of the cathode comprises a noncontiguous thin film of semiconductivc and metallic material deposited at random in small droplets on a substrate and adapted to have a potential difference placed thereacross.

F4l/l/l/l1/lp PATENTEU 0m 5 |97| 361107 7 INVENTOR SIDNEY 7S SMITH ATTORNEY THIN FILM ROOM-TEMPERATURE ELECTRON EMITTER STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of an royalties thereon or therefor.

BACKGROUND OF THE INVENTION The present invention relates generally to vacuum tube devices and more particularly to room temperature electron emission vacuum tubes which require no filament and no filament power.

Those concerned with the development of effective room temperature electron devices have long recognized the need for a practical vacuum device which produces controllable electron emission Such a device eliminates the necessity for filament heat and simplifies the circuitry of any system by obviating the need for a filament power supply.

Technology has heretofore provided numerous devices for the generation of room temperature emission, but they all have serious limitations in either their construction or opera tion which renders them highly unsatisfactory for use as practical design tools. For example, an ultra-light vacuum is necessary for many known devices, while other tubes require elaborate schemes to effectuate normal grid control.

SUMMARY OF THE INVENTION The general purpose of this invention is to provide a room temperature electron emission vacuum tube which embraces all the advantages of similarly employed prior art devices and possesses none of the aforedescribed disadvantages.

It is accordingly one object of the present invention to provide practical room temperature electron emission vacuum tube devices.

One further object is the provision of a vacuum tube device having general utility and requiring no filament power supply.

A still further object is the provision of a vacuum tube having no filament and being easy to construct.

The invention can be summarized as an electrical device comprising a vacuum enclosure containing an anode having a high voltage potential with respect to ground mounted within the enclosure and a cathode mounted within the enclosure in proximity with the anode. The cathode comprises an electrically insulating substrate material upon which is affixed at least two terminals. In one embodiment, a noncontiguous thin film of semiconductive and metallic material is deposited at random in small droplets onto the substrate between the terminals to provide electron emission when a potential difference is applied thereacross. A second embodiment includes a thin film of semiconductive material deposited onto a substrate and having a break therein to thereby produce electron emission.

One advantage of the invention is its ease of construction. In addition, the present device provides effective electron emission and, accordingly, improves the operation of electronic display devices, photocathode night-vision tubes, and the like.

Other objects, advantages, and novel features of the invention will become more fully apparent from the following detailed description of the invention when considered in con junction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates a sectional view of the invention;

FIG. 2A shows a plan view of one embodiment of the electron emitter used in the device of FIG. 1;

FIG. 2B shows a cross-sectional view of the electron emitter taken along line 2B-2B of FIG. 2A looking in the direction of the arrows;

FIG. 3A shows a plan view of a second embodiment of the electron emitter used in the device if FIG. 1; and

FIG. 3B shows a cross-sectional view of the electron emitter taken on line 3B-3B of FIG. 3A looking in the direction of the arrows;

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, there is illustrated in FIG. I a vacuum enclosure 10 which can be constructed from any suitable material, such as glass. The interior of enclosure 10 is maintained at a low vacuum and contains an anode element 12 and a cathode element 14, to be described more fully below. The anode is coupled via lead 16 to a source of high positive electric potential 18. The other end of source 18 is coupled to a common reference point 20 which is further coupled to one electrode 22 of cathode 14 via lead 24. The other electrode 26 of cathode 14 is coupled via lead 28 to variable source 30 to complete the circuit.

One embodiment of the cathode 14 used in the device of FIG. 1 is shown in FIGS. 2A and 2B. In this embodiment, the two electrodes 22 and 26 are affixed to a substrate 32 which may be glass or any other desired material. The electrodes 22 an 26 may be mechanically attached to the substrate 32 or may be deposited thereon by vacuum deposition techniques. Deposited between the electrodes 22 and 26 onto the substrate 32 is a thin continuous film of semiconductive material 34 having a thickness of approximately one micron. Any of various well known semiconductive material can be employed such as silicon, germanium gallium, arsenide, titanium hydride, zirconium hydride, the oxides of alkaline earth metals, etc. By establishinga high electric field across the cathode during its fabrication, a fairly uniform break 35 is produced in the semiconductor film. This break greatly increases the electrical impedance of the cathode and produces a number of microplasmas upon the application of a low potential across the substrate. The potential necessary to maintain these rnicroplasrnas is only a few volts, as compared to the high potential required by the conventional devices, which obviates the necessity for complex heat dissipation schemes. The microplasrnas are theorized as being gaseous discharges and produce a large number of free electrons.

A second embodiment of cathode 14 is shown in FIGS. 3A and 3B. This cathode is identical to the cathode shown in FIGS. 2A and 2B except that a metallic material as well as a semiconductive material are deposited in small droplets 36 onto the surface of the substrate 32. Droplets 36 are deposited in a random fashion such that they form a noncontiguous thin film, covering the exposed surface of the substrate between electrodes 22 and 26. By depositing in turn both semiconductive and metallic droplets in a random fashion onto the substrate surface, a large number of effective semiconductor to metal junctions are formed for electron emission. Such junctions are known to provide barrier layers having correspondingly high fields; however, they have heretofore been impractical due to the difficulty experienced in manufacture. It has been found that effective results can be obtained by the random deposited droplet embodiment of the present invention at a substantial savings.

The theory behind the operation of the present invention will now be explained In the semiconductor-metal droplet embodiment, the primary source of electron emission due to the formation of a large number of small semiconductor-to-metal junctions. By depositing in turn both semiconductor and metal droplets in large numbers, many of the semiconductor droplets will form adjacent to metal droplets at the precise spacing necessary to establish semiconductor-tdmetal junction emission. It is further theorized that the junctions formed by the adjacent semiconductor-metal droplet pairs are more accurately categorized as being transverse field semiconductor-to-metal junction emitters. This is because the plane of the droplet junction is believed to exist perpendicular to the emissive surface. It is noted that in conventional transverse junction emitters, which have been limited to p-n junction types by the difficult construction problems involved, the emission is considered to be inefficient since only the portion of the diode current flowing very close to the surface is of use. In the present invention, however, efficient transverse field emission is provided since the circulating current flow is confined to the surface region of the emitters, and a large number of emitters are provided by the random deposition of droplets. The efficiency of the device is further improved by the fact that those metal and semiconductor droplets which do not form semiconductor-to-metal junctions provide tunneling emission as well as hot electron emission, the theory of which is well known in the art. Thus, the unique and highly simplified construction of the semiconductor-metal droplet embodiment of the present invention provides cold electron emission by a combination of at least three different physical phenomena.

In the second embodiment, the emission produced by the cathode is due to a combination of hot electron emission and gaseous discharge emission. This particular embodiment contains a fairly uniform break in the semiconductor film across its smaller dimension. When a small field is set up by source 30, many small discharges or microplasmas are established to produce electron emission. It is noted that only a small electric field is necessary to maintain the plasma discharge; this is substantially reduces many problems encountered in prior art devices, especially those relating to substrate temperature and electrical breakdown. V

In operation, when variable source 30 in FIG. 1 is applied across the cathode 14, free electrons are produced on the surface of the cathode as explained above. These free electrons are attracted to the anode because of the high positive charge produced thereon by source 18. This flow of electrons from the cathode to the anode establishes a current path across the tube as in conventional filament devices. The current flow produced by the device has many uses; for example, it can be utilized to provide electrical display of information by employing an anode which produces light when struck by electrons. Furthermore, the flow can be effectively controlled by a grid or by the potential source 30 to thereby permit efficient use of the invention as the active element in amplifiers, oscillators, and the like;

Thus, two simple and effective vacuum tube devices are provided which produce electron emission at room temperatures. The devices produce controllable electron emission and can be manufactured with relative ease.

It should be understood, of course, that the foregoing disclosure relates to only the preferred embodiments of the invention and that numerous modifications or alterations may be made thereto in light of the above teachings.

What is claimed and desired to be secured by Letters patent of the United States is:

l. A cold-cathode vacuum tube, comprising:

an enclosure defining a space containing a vacuum;

means mounted within said space for providing emission of free electrons at room temperatures, said means includan electrically insulation substrate,

a thin film of semiconductive material deposited onto said substrate, said film having a uniform break entirely across and substantially parallel to one side thereof, and

means electrically coupled to said thin film for establishing a longitudinal electric field therein in a direction normal to said break; and

means mounted within said space for generating an electric field having a direction normal to the direction of said longitudinal electric field and said break to thereby attract said free electrons.

2. The device of claim 1, wherein said thin film has a thickness of approximately 1 micron.

3. The device of claim 2, wherein said means for generating an electric field having a direction normal to the direction of said longitudinal field and said break, comprises:

a source of high positive electric potential, and

an anode coupled to said source. 4. The device of claim 3, wherein said means for establishing a longitudinal electric field is variable to thereby control the emission of said free electrons.

5. In a vacuum tube, a room temperature electron emitter, comprising:

an electrically insulating substrate;

a thin film of semiconductive material deposited onto said substrate, said thin film having a uniform break entirely across and substantially parallel to one side thereof; and

means electrically coupled to said thin film for establishing a longitudinal electric field therein in a direction normal to said break.

6. The device of claim 5, wherein said thin film has a thickness of approximately 1 micron.

7. The device of claim 6, wherein said means for establishing a longitudinal electric field is variable to thereby control the emission of said free electrons.

8. A cold-cathode vacuum tube, comprising:

an enclosure defining a space containing a vacuum;

means mounted within said space for providing emission of free electrons at room temperatures, said means including:

an electrically insulating substrate,

a plurality of noncontiguous droplets of semiconductive material deposited onto said substrate at random,

a plurality of noncontiguous droplets of metal deposited onto said substrate at random and in contact with said semiconductive material;

means electrically coupled to said substrate for establishing a longitudinal electric field thereacross; and

means mounted within said space for generating an electric field having a direction normal to the direction of said longitudinal electric field to thereby attract said free electrons away from said electron emission providing means.

9. The device of claim 8, wherein said means for generating an electric field having a direction normal to the direction of said longitudinal field, comprises:

a source of high positive electrical potential, and superconducting anode coupled to said source.

10. The device of claim 9, wherein said means for establishing a longitudinal electric field is variable to thereby control the emission of said free electrons.

11. In a vacuum tube, a room temperature electron emitter, comprising:

an electrically insulating substrate;

a plurality of noncontiguous droplets of semiconductive material deposited onto said substrate at random,

a plurality of noncontiguous droplets of metal deposited onto said substrate at random, said metal droplets in contact with said semiconductive material; and

means electrically coupled to said substrate for establishing a longitudinal electric field thereacross.

12. The device of claim 11, wherein said means for establishing a longitudinal electric field is variable to thereby control the emission of said free electrons. 

1. A cold-cathode vacuum tube, comprising: an enclosure defining a space containing a vacuum; means mounted within sAid space for providing emission of free electrons at room temperatures, said means including: an electrically insulation substrate, a thin film of semiconductive material deposited onto said substrate, said film having a uniform break entirely across and substantially parallel to one side thereof, and means electrically coupled to said thin film for establishing a longitudinal electric field therein in a direction normal to said break; and means mounted within said space for generating an electric field having a direction normal to the direction of said longitudinal electric field and said break to thereby attract said free electrons.
 2. The device of claim 1, wherein said thin film has a thickness of approximately 1 micron.
 3. The device of claim 2, wherein said means for generating an electric field having a direction normal to the direction of said longitudinal field and said break, comprises: a source of high positive electric potential, and an anode coupled to said source.
 4. The device of claim 3, wherein said means for establishing a longitudinal electric field is variable to thereby control the emission of said free electrons.
 5. In a vacuum tube, a room temperature electron emitter, comprising: an electrically insulating substrate; a thin film of semiconductive material deposited onto said substrate, said thin film having a uniform break entirely across and substantially parallel to one side thereof; and means electrically coupled to said thin film for establishing a longitudinal electric field therein in a direction normal to said break.
 6. The device of claim 5, wherein said thin film has a thickness of approximately 1 micron.
 7. The device of claim 6, wherein said means for establishing a longitudinal electric field is variable to thereby control the emission of said free electrons.
 8. A cold-cathode vacuum tube, comprising: an enclosure defining a space containing a vacuum; means mounted within said space for providing emission of free electrons at room temperatures, said means including: an electrically insulating substrate, a plurality of noncontiguous droplets of semiconductive material deposited onto said substrate at random, a plurality of noncontiguous droplets of metal deposited onto said substrate at random and in contact with said semiconductive material; means electrically coupled to said substrate for establishing a longitudinal electric field thereacross; and means mounted within said space for generating an electric field having a direction normal to the direction of said longitudinal electric field to thereby attract said free electrons away from said electron emission providing means.
 9. The device of claim 8, wherein said means for generating an electric field having a direction normal to the direction of said longitudinal field, comprises: a source of high positive electrical potential, and superconducting anode coupled to said source.
 10. The device of claim 9, wherein said means for establishing a longitudinal electric field is variable to thereby control the emission of said free electrons.
 11. In a vacuum tube, a room temperature electron emitter, comprising: an electrically insulating substrate; a plurality of noncontiguous droplets of semiconductive material deposited onto said substrate at random, a plurality of noncontiguous droplets of metal deposited onto said substrate at random, said metal droplets in contact with said semiconductive material; and means electrically coupled to said substrate for establishing a longitudinal electric field thereacross.
 12. The device of claim 11, wherein said means for establishing a longitudinal electric field is variable to thereby control the emission of said free electrons. 